墩周绕流对抛石落距的影响

Flow-affected riprap transport distance around circular pier in the deposition process

动水中抛石常用于桥墩冲刷的应急防护。受墩周水流的影响,抛石沉降的着床点难以确定。本文研究了抛石落距受水流、桥墩绕流及抛石颗粒特性的影响规律,用量纲分析法建立了相关物理方程,通过大量多因素的水槽试验,观测了桥墩绕流不同区域抛石落距规律,确定了方程式的系数及指数。各项试验均多次重复,对观测数据均进行了统计分析,以避免试验观测错误。研究表明,抛石落距与水流Fr数及水深h成正比,与抛石颗粒和水的相对密度差(ρs-ρ)/ρ及颗粒尺度dr成反比,并与墩雷诺数有关。墩周绕流阻力导致墩前抛石落距较均匀流条件下减小,绕流影响区内、外落距明显不同。

Riprapping is often used to protect pier scour in case of emergency. Affected by the flows around the pier, it is difficult to determine its dropping position. Flume experiments were performed to in- vestigate the impacts of the flow parameters, flow regime around the circular pier, and the riprap character- istics on riprapping process. Dimensional analysis was used to establish a reasonable non-dimensional equa- tion, in which the coefficient and exponents were estimated by the experiment data. In order to avoid poten- tial measurement errors, each set of the experiments was repeated for 100 times and the data were ana- lyzed by rigorous statistical model. The results indicate that riprap moving distance increases with Fr num- ber and water depth, h, and decreases with the relative density difference of riprap and fluid, （ps-p）/p, as well as the riprap size, dr. Pier Reynolds number, Rep, affects the moving distance when a riprap approach- es the pier. Thus, riprap moving distance is shorter in a flow area around pier than that in uniform flow.